Method and arrangement for minimizing skew

Abstract

At a signal transmission rate of 1 Gb/s, the "bit time" is 1 ns. This corresponds to a bit length in an optical fibre of 0.2 m. In view of the fact that skew shall not exceed one-tenth of a bit length, this means that length differences between different conductors in a transmission line may not exceed 2 cm. With the intention of minimizing the skew that would thus otherwise occur in a transmission line, the transmission line (1) and its conductors (2) have been joined to form a ribbon cable or flat cable where the length difference (5) between different conductors (2) in the transmission line does not exceed 2 cm. By providing transmission lines, such as rolled-up flat ribbon cables for instance, which have been previously cut to precise and appropriate lengths, such as lengths of 10, 20, 30 m for instance, with a largest length deviation between different conductors of ±1 cm, skew can be minimized when using the cables. By conductor is primarily meant an optical fiber, although other conductors such as coaxial conductors or twin wire conductors are conceivable. Since the three fibres are seated together along the major part of their lengths, they can be readily laid in an installation, which is an advantage in many types of installations, and the cable parts can be easily drawn apart and laid individually. With a guaranteed greatest length deviation of ±1 cm of each fibre, skew can be controlled and more reliable signal transmission made possible with the aid of a majority decision.

We claim: 
     
       1. A method of minimizing skew in the ultra high-speed transmission of information, comprising the steps of: fixating three or more conductors in a mutually parallel and spaced relationship so that any differences in lengths between the conductors does not exceed a greatest value such that a skew does not exceed a part of a bit slot when each of the conductors transmits substantially a same information;   transmitting simultaneously and in parallel the substantially the same information via each of said conductors; and   taking a majority decision of the substantially the same information transmitted via each of said conductors to avoid a bit error.   
     
     
       2. The method according to claim 1, wherein the part of a bit slot is a tenth of a bit slot. 
     
     
       3. The method according to claim 1, the conductors being optical fibers. 
     
     
       4. A method for reducing skew associated with the transmission of information over a plurality of conductors comprising the steps of: providing at least three conductors in a substantially fixed and parallel relationship;   establishing a length of each of said at least three conductors such that a time deviation between corresponding bits transmitted via each of said at least three conductors is less than a predetermined portion of a bit slot;   transmitting corresponding bits via each of said at least three conductors; and   taking a majority decision of said corresponding bits transmitted via each of said conductors.   
     
     
       5. The method according to claim 4, wherein said predetermined portion is a tenth of a bit slot. 
     
     
       6. The method according to claim 4, the conductors being optical fibers. 
     
     
       7. A method of transmitting information comprising the steps of: providing at least three conductors in a substantially fixed and parallel relationship;   establishing a length of each of said at least three conductors such that a time deviation between corresponding bits transmitted via each of said at least three conductors is reduced to less than a predetermined portion of a bit slot;   transmitting corresponding bits via each of said at least three conductors; and   taking a majority decision of said corresponding bits, said reduced time deviation lessens an error associated with said majority decision.   
     
     
       8. The method according to claim 7, the conductors being optical fibers.